Q:I am allergic to sulfur. Can I take MSM?
A:Strictly speaking, the concept of a “sulfur allergy” is a misconception: sulfur is an element, the third most abundant mineral in the human body. It's not possible to be allergic to sulfur because it has no protein component.
When people say they are "allergic to sulfur", what they really mean is that they are allergic or sensitive to certain sulfur-containing substances, most notably to sulfa antibiotics (sulfonamides) or to sulfites (preservatives used in wines and some foods), or to foods with a high sulfur content (broccoli or cauliflower).
Many individuals with allergies to sulfa drugs or to sulfites do not experience problems taking MSM, because apart from sulfur, MSM bears no relation to these substances.
However, people who are allergic to one drug are more likely to be allergic to another, regardless of its chemical structure. So if you have a known allergy to sulfonamides or to sulfites, consult with your physician before taking MSM.
http://www.msmguide.com/facts/faq/
Q: Is sulfur the same as sulfa drugs and sulfites? I'm allergic to sulfites. Does this mean I will be allergic to MSM?
A: Do not get confused between the two. MSM provides organic sulfur and is a nutrient. Sulfa-based drugs, also known as sulfonamides, do not occur naturally and are used as antibiotics.
The sulfa molecule is much larger and can cause severe reactions in some individuals. An estimated half-million people are sulfite sensitive in the US. Most often they are asthmatic adults and predominantly women.
While many people are allergic to sulfa drugs, no similar reactions have ever been reported with MSM.
A third sulfur-containing compound, known as sulfites, is a form of preservative that can cause allergic reactions in some individuals. MSM does not contain sulfites, and should not cause a reaction in sulfite-sensitive individuals.
The human body produces sulfites in its normal metabolism of sulfur-containing amino acids. Sulfite compounds have been used for more than three hundred years and are generally considered safe.
http://www.nwhealthsolutions.com/msmfaq.htm